bpo-34108: Fix double carriage return in 2to3 on Windows (python#8271)

jaraco · web-flow · commit cafaf0447b95 · 2018-07-13T11:26:03.000-04:00
* Add test capturing failure.
* Honor newlines as present in the original file.
diff --git a/Lib/lib2to3/refactor.py b/Lib/lib2to3/refactor.py
@@ -514,7 +514,7 @@ def write_file(self, new_text, filename, old_text, encoding=None):
         set.
         """
         try:
-            fp = io.open(filename, "w", encoding=encoding)
+            fp = io.open(filename, "w", encoding=encoding, newline='')
         except OSError as err:
             self.log_error("Can't create %s: %s", filename, err)
             return
diff --git a/Lib/lib2to3/tests/test_refactor.py b/Lib/lib2to3/tests/test_refactor.py
@@ -300,6 +300,7 @@ def test_crlf_unchanged(self):
         old, new = self.refactor_file(fn)
         self.assertIn(b"\r\n", old)
         self.assertIn(b"\r\n", new)
+        self.assertNotIn(b"\r\r\n", new)
 
     def test_refactor_docstring(self):
         rt = self.rt()
diff --git a/Misc/NEWS.d/next/Library/2018-07-13-08-44-52.bpo-34108.RjobUC.rst b/Misc/NEWS.d/next/Library/2018-07-13-08-44-52.bpo-34108.RjobUC.rst
@@ -0,0 +1 @@
+Remove extraneous CR in 2to3 refactor.
